New 220 4 wire stove and old 220 three wire plug

I have started a kitchen remodel where we are replacing all the appliances. The old double ovens were 220 with a three prong plug. The new ovens are four wire. Can the four wire be wired wired into a three prong plug and use a grounding strap on the neutral at the ovens? Do I need to have the house rewired with four wires back to the mains?

For existing branch circuit installations there is an Exception to NEC 250.140 that permits you to use a 3-wire cord and to connect the frame of the range to the grounded conductor (the neutral) if all of the following conditions are met:

1. It is a 120/240-volt single phase 3-wire, or a 208Y/120-volt derived from 3-phase Y system.

2. The grounded conductor (neutral) is not smaller than #10 copper or #8 aluminum.

3. The grounded conductor is insulated, or if not insulated is part of a Type SE service-entrance cable and the branch circuit originates at the service panel.

4. Grounding contacts of receptacles furnished as part of the equipment are bonded to the equipment.

Thanks for the info. The house was built in 1965 and the electrical is original. The three prong receptacle has a red, a black and a green wire dedicated back to a dual breaker at the main entrance panel on the side of the house.

Thanks for the info. The house was built in 1965 and the electrical is original. The three prong receptacle has a red, a black and a green wire dedicated back to a dual breaker at the main entrance panel on the side of the house.

I think the question here is not whether he can use the (existing) neutral as a ground, but rather whether he can use the (existing) ground as a neutral. Having said that, I'm not enough of a Code scholar to say yes or no, although it strikes me that the end result is electrically, if not artistically, identical.

The conditions of the exception to 250.140 that are relevant to the third wire are:

2. The grounded conductor is not smaller than 10 AWG copper or 8 AWG aluminum.

3. The grounded conductor is insulated, or the grounded conductor is uninsulated and part of a Type SE service-entrance cable and the branch circuit originates at the service equipment.

The fact that the third conductor is reported as green indicates that it meets the first option of condition 3, which is sufficient for the exception.

It is likely that the wire available in 1965 was either the SE cable with red, black, and spiral-wrapped grounded conductor, or the NM that was red, black, and green, or NM that was black, white, and green, or NM that was black, white, and bare.

The green wire is obviously insulated and appears to comply with the provisions of the exception which says nothing about color.

Wow I now realize I know squat about this stuff. I think my best bet would be to have an electrician come in and wire it to code. At least that way, I know it will be right and compliant with the latest safety measures.

All stoves built today are built to use a 4-wire hookup: two hots, a neutral, and a safety ground. Neutral and ground are connected back at or near the panel. It is safest if there is a real ground at the appliance, rather than the neutral which could get loose, or come off, or be broken accidentally. That way, you really do have a margin of safety.

All stoves built today are built to use a 4-wire hookup: two hots, a neutral, and a safety ground. Neutral and ground are connected back at or near the panel. It is safest if there is a real ground at the appliance, rather than the neutral which could get loose, or come off, or be broken accidentally. That way, you really do have a margin of safety.

Click to expand...

Not to start anything, but why would a nuetral have any more of a chance to come loose or break than a ground? The ground on a 6/3 is #10 if not mistaken.

My understanding was that in the past, before all of the bells and whistles on stoves, neutrals were not needed. It was a 220volt. Now that a 110 circuit is required in some new stoves, a neutral is needed.

How many stoves do you know of that don't have either a lamp, or an accessory plug? Those use 110vac, so require the neutral. Only the heating elements are 220vac, not any of the peripherals. Having both a neutral and a ground gives some redundency and safety. If you lost a neutral, you might blow up some of the electronics or the bulb, depending on how it was wired since it might see 220, but...

How many stoves do you know of that don't have either a lamp, or an accessory plug? Those use 110vac, so require the neutral. Only the heating elements are 220vac, not any of the peripherals. Having both a neutral and a ground gives some redundency and safety. If you lost a neutral, you might blow up some of the electronics or the bulb, depending on how it was wired since it might see 220, but...

Click to expand...

Well, back in the day they might have not had a plug or an acessory outlet. If it had a bulb, it could have been rated for 240.... just a thought.

Ever tried to buy a 240v light bulb...not in your everyday store! If they had a bulb, oven light, night light, indicator light, etc., they were powered off 110. When I was in the Army, we had one shelter with both 28vdc and 110vac lighting. The bulbs were the same style. If you weren't careful, the 28V bulbs work great as flash bulbs! Working the other way, they worked more like a candle, which isn't catastrophic, but kind of useless.

Notwithstanding all "The sky will fall on your head" remarks, the National Electrical Code explicitly permits, for existing branch circuit installations, "the frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlets or junction boxes that are part of the circuit for these appliances" to be grounded to the grounded circuit conductor if all of the conditions that I posted earlier are met.

A couple of red flags come to surface with this installation and the insulated GREEN conductor raises a flag to its highest.

If this circuit installation has an insulated green conductor it must be wired with some type of cord. I all my years I canâ€™t remember seeing a SE cable or NM cable that had an insulated green conductor that came installed in the cable. The use of a cord as a permanent wiring method is a big no no.

If this installation is done in some sort of metal jacketed cable such as MC or AC then the use of a three wire receptacle is NOT allowed.

In the end the one thing to remember is that if a three wire receptacle is used then any and all exposed metal of the range will be at the same potential as the conductor carrying the unbalanced load.
In other words the exposed metal will be at a potential of 120 volts anytime that the clock or oven light is energized.

In the end the one thing to remember is that if a three wire receptacle is used then any and all exposed metal of the range will be at the same potential as the conductor carrying the unbalanced load.In other words the exposed metal will be at a potential of 120 volts anytime that the clock or oven light is energized.

Click to expand...

That (the bolded part of the quote) is just plain WRONG. It will be at a potential equal to the voltage drop in the ungrounded conductor that arises from the IR drop of the unbalanced current, which is the same condition that has existed on ranges, ovens, and dryers for as long as they have had lights and clocks.

With 1 Amp which would be typical of a light, and a 50 ft run to the panel, the potential will be about 0.06 Volt, about 1/25 of the voltage of an alkaline battery. Even if the there were a 100 Amp dead short to the grounded conductor, which would quickly trip the breaker, the voltage would be about 6 Volts which is far below the hazardous level.

That (the bolded part of the quote) is just plain WRONG. It will be at a potential equal to the voltage drop in the ungrounded conductor that arises from the IR drop of the unbalanced current, which is the same condition that has existed on ranges, ovens, and dryers for as long as they have had lights and clocks.

Click to expand...

It has been a long day trying to bring my current classes up to the 08 code cycle.

The touch potential would put the person in parallel with the clock and or light. In other words the person could become a parallel path with the current these items draw.

Touching the frame of the range and such items as grounded crock pots made from stainless steel to large bowl mixers could lead to a shocking experience.